Who discovered black hole Theory?

IT has been a long discussion o gravity but at first Albert Einstein general theory of relativity (published in 1916) predicts black holes. Then a few months after Karl Schwarzschild gave a solution for the gravitational field of a point mass and a spherical mass, that a black hole could theoretically exist.
Still it is being said that Black Holes are purely theoretical and for them to exist goes against basic physics. Nobody has ever seen black hole. If a stars gravity was to strong it would explode and not form a black hole according to basic laws and physics.